Sand filled - SF{HD 6 {B fused bushing

ABSTRACT

A fused high voltage electric bushing for connecting a high voltage cable to an electrical apparatus within a casing, the bushing including a dielectric housing, an electrical terminal sealed to each end of the housing, a fusible element within said housing electrically connected to each of said terminals, a granular dielectric material within said housing and a gaseous insulating medium completely filling said housing, the medium being sulfur hexalfluoride (SF6). A layer of thermally insulating material can be provided on the inside surface of said housing.

United States Patent [191 Mikulecky [451 Nov. 18, 1975 SAND FILLED SFFUSED BUSHING [75] Inventor: Harvey W. Mikulecky, Racine, Wis.

[73] Assignee: RTE Corporation, Milwaukee, Wis.

[22] Filed: Apr. 29, 1974 [21] Appl. No.: 465,332

[52] US. Cl. 337/202; 337/224; 337/279 [51] Int. Cl. H01H 85/18 [58]Field of Search 337/202, 273, 277, 279,

[56] References Cited UNITED STATES PATENTS v 2,539,261 l/l951 Miller337/279 2,593,426 4/1952 Fahnoe 337/279 2,981,815 4/1961 Leeds et al.174/31 R 3,633,141 l/l972 Ristuccia 337/202 3,648,211 3/1972 McKeithan337/202 Primary Examiner-Harold Broome Attorney, Agent, or FirmRonald E.Barry [57] ABSTRACT A fused high voltage electric bushing for connectinga high voltage cable to an electrical apparatus within a casing, thebushing including a dielectric housing, an electrical terminal sealed toeach end of the housing, a fusible element within said housingelectrically connected to each of said terminals, a granular dielectricmaterial within said housing and a gaseous insulating medium completelyfilling said housing, the medium being sulfur hexalfluoride (SP A layerof thermally insulating material can be provided on the inside surfaceof said housing.

A 10 Claims, 1 Drawing Figure US. Patent Nov. 18, 1975 3,921,116

I if, E

SAND FILLED SF FUSED BUSHING BACKGROUND OF THE INVENTION In my copendingapplication entitled A Heat Insulating Fused High Voltage Bushing, Ser.No. 385,436, filed Aug. 3, 1973 and assigned tothe same assignee, and inthe copending application of Edwin A. Link, Ser. No. 275,178, filed July26, 1972 and assigned to the same assignee, current limiting fusedbushings are disclosed which are designed for use at voltages of 8.3KV.This bushing also included a thermal insulating barrier which was usedto protect the housing from thermal shock on vaporization of the fuseelement. A resistive coating is placed on the inside surface of thebushing to minimize voltage stresses and to hold the radio influencevoltage (RIV) down to an acceptable level. This type of bushing provedsatisfactory at design voltage. However, the higher KV ratings providehigher voltage stresses which results in a further increase in the radioinfluence voltage.

SUMMARY OF THE PRESENT INVENTION hexafluoride (SE or one of a number ofsimilar inert gases. These dielectric gases can withstand a much highervoltage stress without producing corona.

Other objects and advantages of the invention will become more apparentfrom the following description when read in conjunction with the drawingin which a sectional elevation view of the invention is shown.

DESCRIPTION OF THE INVENTION Referring to the drawing, the fused highvoltage bushing 10 is shown mounted in an opening 12 in the casing 14for an electrical device such as a transformer.

The casing 14 is normally filled with a dielectric fluid I or insulatingoil 16 with the lower end of the bushing :10 extending into the oil 16'.The bushing 10 is retained close the passage 27 by means of a gasket 33.The bushing 10 is connected to the electrical apparatus by means of theelectric terminal 32 provided at the inner end of the bushing. Theterminal 32 is sealed to the inner end of the passage 27 by means of agasket 38.

The voltage stress at the point of entrance of the bushing 10 throughthe casing 14 can be reduced by providing a layer of electricallyconductive material on the inside of passage 27 as described incopending application Ser. No. 385,436. The material can be a conductiveglaze or a conductive epoxy paint or any other conductive material whichcan be used for this purpose. The layer 40 extends through a portion ofthe length of the passage 27 and should pass through the opening 12 inthe casing 14. Means can be provided for connecting the layer 40 to oneof the electrical terminals 30 or 32 in the form of a conductive member42.

Means can also be provided for reducing the voltage stress in theopening 12 in the casing in the form of a conductive layer 42 providedon the outer surface of the housing 25. The layer 40 extends through theopening 12 a sufficient distance to be immersed in the dielectric fluid16. The conductive layer 42 can be in the form of a conductive glaze ora conductive epoxy paint. The upper layer of the conductive layer 42 isgrounded in casing 14 by means of the mounting assembly 18.

The passage 27 can be thermally insulated by means of a heat insulatinglayer 44 provided on the inside surface of the passage 27. The layer 44is shown in the form of a sleeve which has an outer diametersubstantially equal to the inner diameter of the passage 27. The passage27 is filled with a granular dielectric material 34. The sleeve 44 ispositioned between the granular dielectric material 34 and the insidesurface of the passage 27 to insulate the housing from the heat of theare in the casing 14 by means of a mounting assembly 18 and is sealed inthe opening by means of a gasket 20.

This is basically the same arrangement as shown in my copendingapplication Ser. No. 385,436 except for an increase in fuse length inaccordance with the higher voltage.

The bushing 10 includes an insulating housing 25 having a centralpassage 27 and a fuse assembly 22 po- 7 sitioned in the passage 27. Theassembly 22 includes a first fusible element 24 generally in the form ofa silver :wire or ribbon spirally wrapped around a spindle .28

and a second fusible element or expulsion fuse 26 connected in serieswith the element 24. The first fusible v element 24 provides a highcurrent interruption capability. The second fusible element provides alow cur- I -rent interruption capability. The fuse assembly 22 is fusingof the elements 24 and 26.

The bushing 10 is connected to a high voltage cable by means of aterminal casting 31 screwed onto the electric terminal 30 provided onthe end of the housing 25. The terminal casting 31 is sealed to thehousing to from the bushing. The passage is then back filled withproduced on fusing of the element 24. The sleeve 44 can be formed fromany of the known heat insulating materials such as asbestos.

In accordance with the invention, the radio influence voltage is reduced'by providing a gaseous insulating medium of high dielectric strengthwithin the passage 27. This is accomplished by removing the terminalcasting 31 and gasket 33 from the housing 25 and pulling a vacuum withinthe passage 27 to remove all of the air sulfur hexafluoride (SP to equalor slightly higher pressure than normal atmospheric pressure. Theterminal casting 31 and gasket 33 are then replaced'on the housing toseal the sulfur hexafluoride within the passage. I Y

7 Although sulfur hexafluoride has been shown as the preferred material,a number of other gaseous materials can also be used such ashexafluoroethane (C 1 perfluorocyclobutane (C F dichlorodifluoromethane(CF CL chloropentafluoroethane (CF CLCF and bromotrifluoromethane (CFBR).

I claim: I 1. A fused high voltage electrical bushing for connecting ahigh voltage cable to an electrical device housed within a casing, saidbushing comprising:

a housing formed of a dielectric material having an axially extendingpassage, an electric terminal sealed to each end of said passage todefine a closed chamber, a fusible assembly within said chamberelectrically connected to each of said terminals,

a layer of conductive material on the inside surface of said passage forreducing the voltage stress at the point of entrance of the bushingthrough the casing, i

a granular dielectric material completely filling said chamber,

and an inert gaseous insulating medium completely filling said chamberto minimize the occurrence of corona within said granular dielectricmaterial.

2. The bushing according to claim 1 wherein said fusible assemblycomprises a first fusible element of high current interruptingcapability and a second fusible element of low current interruptingcapability, said first and second elements being connected together toform a series circuit, said layer of material on the inside surface ofsaid passage enclosing only the first fusible element.

3. The bushing according to claim 1 wherein said insulating medium issulfur hexafluoride.

4. The bushing according to claim 1 wherein said insulating medium isselected from the group consisting of sulfur hexafluoride, hexafiuoroethane, perfluorocyclobutane, dichlorodifluoroethane,chloropentafluoroethane and bromotrifluoromethane.

5. The bushing according toclaim 3 including a layer of insulatingmaterial on the surface of said passage.

6. The bushing according to claim 5 includingmeanson the outside surfaceof the bushing for reducing voltage stress at the point of entrance ofthe bushing through the casing.

7. A fused high voltage electrical bushing for connecting a high voltagecable to an electrical device housed within a casing, said bushingcomprising a housing formed of a dielectric material having an axiallyextending passage,

an electric terminal sealed to each end of said passage,

a fusible assembly positioned within said passage and electricallyconnected to each of said terminals, a layer of conductive material onthe inside surface of said passage,

a layer of thermally insulating material on the inside surface of saidconductive material,

a granular dielectric material completely filling said chamber,

and an inert gaseous medium completely filling said chamber to minimizethe occurrence of corona within the granular dielectric material.

8. The bushing according to claim 7 wherein said fusible assemblycomprises a first fusibleelement of high current interrupting capabilityand a second fusible element of low current interrupting capability,said first and second elements being connected together to form a seriescircuit, said layer of material on the inside surface of said passageenclosing only the first fusible element. I 1 v 9. The bushing accordingto claim 8 wherein said insulating medium is sulfur hexafluoride.

10. The bushing according to claim 8 wherein said insulating medium isselected from the group consisting of sulfur hexafluoride,hexafluoroethane, perfluorocyclobutane, dichlorodifluoroethane,

fluoroethane and bromotrifluoromethane.

chloropenta-

1. A fused high voltage electrical bushing for connecting a high voltagecable to an electrical device housed within a casing, said bushingcomprising: a housing formed of a dielectric material having an axiallyextending passage, an electric terminal sealed to each end of saidpassage to define a closed chamber, a fusible assembly within saidchamber electrically connected to each of said terminals, a layer ofconductive material on the inside surface of said passage for redUcingthe voltage stress at the point of entrance of the bushing through thecasing, a granular dielectric material completely filling said chamber,and an inert gaseous insulating medium completely filling said chamberto minimize the occurrence of corona within said granular dielectricmaterial.
 2. The bushing according to claim 1 wherein said fusibleassembly comprises a first fusible element of high current interruptingcapability and a second fusible element of low current interruptingcapability, said first and second elements being connected together toform a series circuit, said layer of material on the inside surface ofsaid passage enclosing only the first fusible element.
 3. The bushingaccording to claim 1 wherein said insulating medium is sulfurhexafluoride.
 4. The bushing according to claim 1 wherein saidinsulating medium is selected from the group consisting of sulfurhexafluoride, hexafluoroethane, perfluorocyclobutane,dichlorodifluoroethane, chloropentafluoroethane andbromotrifluoromethane.
 5. The bushing according to claim 3 including alayer of insulating material on the surface of said passage.
 6. Thebushing according to claim 5 including means on the outside surface ofthe bushing for reducing voltage stress at the point of entrance of thebushing through the casing.
 7. A fused high voltage electrical bushingfor connecting a high voltage cable to an electrical device housedwithin a casing, said bushing comprising a housing formed of adielectric material having an axially extending passage, an electricterminal sealed to each end of said passage, a fusible assemblypositioned within said passage and electrically connected to each ofsaid terminals, a layer of conductive material on the inside surface ofsaid passage, a layer of thermally insulating material on the insidesurface of said conductive material, a granular dielectric materialcompletely filling said chamber, and an inert gaseous medium completelyfilling said chamber to minimize the occurrence of corona within thegranular dielectric material.
 8. The bushing according to claim 7wherein said fusible assembly comprises a first fusible element of highcurrent interrupting capability and a second fusible element of lowcurrent interrupting capability, said first and second elements beingconnected together to form a series circuit, said layer of material onthe inside surface of said passage enclosing only the first fusibleelement.
 9. The bushing according to claim 8 wherein said insulatingmedium is sulfur hexafluoride.
 10. The bushing according to claim 8wherein said insulating medium is selected from the group consisting ofsulfur hexafluoride, hexafluoroethane, perfluorocyclobutane,dichlorodifluoroethane, chloropentafluoroethane andbromotrifluoromethane.